Electric tools such as cordless screwdrivers are constantly being further developed and optimized with regard to the needs of the user, and in particular easy handling and, often, a compact design are sought. At the same time, the electric motor built into the electric tool should adequately meet demands regarding power and torque resulting from particular applications. These facts present challenges for product design and the selection of a suitable production process.
A typical electric motor for an electric tool standardly has a stator having coil windings and a three-phase terminal. A maximally efficient coil winding of the electric motor is to be provided, a pin winding method typically being used. In standard stator coils, only a low number of windings is required due to high rotation numbers. In order to fill the group surface with as much copper as possible given the relatively low number of windings, the copper wire diameter increases. However, the possible wire diameter is limited by the pin winding process. Furthermore, the number of windings decreases when all coils of a phase are connected in series, because in this case the induced voltages would sum. For this reason, a parallel connection of the coils is preferred. Due to the reduced wire diameter in the case of a parallel connection, a more advantageous winding topology can be realized with which the groove can be maximally filled.
European Patent No. EP 2849316 A2 describes an electric motor for an electric tool that has, for each phase terminal, a multiplicity of coils connected in parallel, and has the same number of connection terminals for the coils, the connection terminals being connected to the external line terminals through a multiplicity of wiring layers, by a circuit board and connecting pieces.
Thus, there is a need to provide a winding schema for concentrated coils, connected in parallel, of an electric motor, in particular for an electric tool, in which production is simplified and costs are saved.